Winter actually causes more damage to diesel trucks than most owners think. Every year problems like gelled fuel, failure to start or weak start, longer warm-up time and even cut short regeneration cycles show up in diesel trucks that are exposed to cold. However, the Cummins engine copes with cold better than most diesel engines but "better than most" still leaves space for major problems when the temperature goes below zero.
Those trucks that start without fail even at minus 20 and run smoothly throughout the winter are not the typical models. They have a handful of targeted modifications that fix the issues cold weather brings out. None of those changes is beyond the reach of a normal person, and actually, most of them can pay for themselves through one winter by avoiding a tow, a gelled fuel system, or an engine breakdown.
In case you live in an area that has a harsh winter, these are the upgrades that you should consider doing before the first hard freeze, rather than after you are left in a parking lot waiting for the fuel to thaw.
The heater integrated with the engine block on a Cummins works up to a point; however, many owners are either inconsistent in their usage or do not even realize the drastic impact that cold weather can have on starting a vehicle, even if the heater is connected. Diesel engines ignite fuel using the heat generated by compression, and if the block is sufficiently cool, the temperature of the compressed air at the end of the piston stroke is not high enough to ensure a reliable ignition of the fuel-air mixture.
If a block heater is connected to the power supply for around three to four hours prior to starting, it can be a night-and-day difference when the temperature is below 20 degrees Fahrenheit. If the temperature drops below zero, a block heater is no longer a luxury. Even if the engine can be turned on without it, you will be spinning the starter, draining the batteries, and the fuel will be washing down the cylinder walls while the engine finally manages to run. Such wear and tear can be easily prevented by simply using an extension cord and a timer.
The Cummins has a grid heater that heats the intake air to the engine before starting to prevent cold starts. It is different from glow plugs that need one per cylinder since the grid heater is only one electric element that will heat all the intake air entering the cylinders. When it is working, it works great. However, when it fails, cold starts will be quite challenging.
It is not often that the heater itself will be the problem, but it is common for the electrical connections and relays that control the heater to be the problem. As a result of the large current being drawn by the heater, the terminals are corroded over time, and a bad connection means that the heater will not be working at full capacity even if the dashboard light shows that it is. Many complaints about hard starting in winter are traced back to the grid heater's electrical issues rather than to the element itself.
It is quite cheap to run the grid heater relay and connections check as part of winter preparation. If the terminals seem to be corroded or the relay is original to a truck with high mileage, it is justifiable to replace both as the cost is minimal. The grid heater that is working properly, in combination with a block heater, would ensure a starting engine almost immediately even in very cold weather.
Diesel fuel gels in cold weather because the paraffin wax in the fuel solidifies and blocks the fuel filters. Most gas stations sell winter fuel treated for cold regions, but the treatment level varies, and trucks that are parked for a few days in extreme cold can gel up even on winter-blend fuel.
Using a good anti-gel agent with each fill-up during winter is the most cost-effective solution you can get. Brands like Stanadyne, Power Service, and Howes all do the job, and they will cost you about fifty cents per tank. The price of one frozen fuel filter in a parking lot at 10 below after all is many times more than a season's worth of additive.
Replacing fuel filters at regular intervals becomes more important in winter. A filter that is close to its service life will gel up sooner than a new one, so changing fuel filters in the fall before the cold weather sets in is definitely worth the small effort. Sourcing quality winter-ready filters from diesel specialists like Diesel Patriots is a simple way to stay ahead of gelling issues, and bringing along a spare filter in the truck is also a good idea, especially if you are driving long distances in winter.
It is quite a complex matter how the 6.7L Cummins emissions system reacts to cold weather, and the details are worth knowing. When it is cold, regeneration processes take more time since the exhaust is slower in heating up. Besides, short trips during winter which do not allow a regeneration process to be completed result in continued soot loading until a warning light is shown or a forced regeneration is demanded.
DEF fluid also freezes at temperatures below 12 degrees Fahrenheit. The system is intended to thaw it when the vehicle is started by using heated lines and a heated tank, but when parts fail, a frozen DEF system will generate error codes, and finally, the truck will go into limp mode. Winter cold-related DEF problems are among the most frequent complaints from owners of late-model Cummins trucks.
For trucks used off-road or in competition where emissions equipment isn't required, some owners find delete kit options to remove these systems entirely, which eliminates the cold-weather failure modes. If that's the direction you're going for an off-road truck, you can find delete kit packages built specifically for the various Cummins generations. As always, this path is for off-road and competition use only, and owners are responsible for understanding the laws that apply to their truck.
A stuck-open thermostat can be pretty challenging to identify during summer and if not found before winter, it could be really uncomfortable. Your engine won't warm up to the standard operating temperature, the heater barely gives you any heat, and you will even notice a decrease in your fuel consumption efficiency as the engine is running richer to make up for the cold operation. You can always test your thermostat before it turns cold or replace it on your high-mileage trucks without waiting for it to get bad as it is a kind of insurance.
Moreover, coolant should not be neglected either. Factory coolant can last for a certain number of miles or years only and once it is over the limit, the coolant will no longer have the ability to protect from freezing and the inhibitors that prevent corrosion will also be depleted. To avoid freeze damage and at the same time keep the cooling system so healthy that it can do its real job, it is always good to get the coolant tested or just change it at regular intervals.
Winter shows every flaw in a truck however, a Cummins will respond well if winter preparation is done in a proper manner. A truck with a functioning block heater, batteries in good condition, a clean fuel system, and an emissions system in good working order will start without a problem, perform well, and avoid the quite expensive breakdowns that will surprise owners who are the least prepared. Most of this is not hard at all and the cost is trivial in comparison with the alternative. It is always more economical to get ready for winter than to have to deal with it unexpectedly.
